Flexible memory system with a controller and a stack of memory

ABSTRACT

Embodiments of a system and method for providing a flexible memory system are generally described herein. In some embodiments, a substrate is provided, wherein a stack of memory is coupled to the substrate. The stack of memory includes a number of vaults. A controller is also coupled to the substrate and includes a number of vault interface blocks coupled to the number of vaults of the stack of memory, wherein the number of vault interface blocks is less than the number of vaults.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No.15/620,490, filed Jun. 12, 2017, which is a continuation of U.S.application Ser. No. 13/919,503, filed Jun. 17, 2013, now issued as U.S.Pat. No. 9,679,615, which claims the benefit of priority to U.S.Provisional Application Ser. No. 61/791,182, filed Mar. 15, 2013, all ofwhich are incorporated herein by reference in their entirety.

BACKGROUND

Memory bandwidth has become a bottleneck to system performance inhigh-performance computing, high-end servers, graphics, and (very soon)mid-level servers. Microprocessor enablers are doubling cores andthreads-per-core to greatly increase performance and workloadcapabilities by distributing work sets into smaller blocks anddistributing them among an increasing number of work elements, i.e.cores. Having multiple computer elements per processor results in anincreasing amount of memory per computer element. This results in agreater need for memory bandwidth and memory density to be tightlycoupled to a processor to address these challenges. Current memorytechnology roadmaps do not provide the performance to meet the centralprocessing unit (CPU) and graphics processing unit (GPU) memorybandwidth goals.

To address the need for memory bandwidth and memory density to betightly coupled to a processor, a hybrid memory cube (HMC) may beimplemented so that memory may be placed on the same substrate as acontroller enabling the memory system to perform its intended task moreoptimally. The HMC may feature a stack of individual memory dieconnected by internal vertical conductors, such as through-silicon vias(TSVs), which are vertical conductors that electrically connect a stackof individual memory die with a controller, such as to combinehigh-performance logic with dynamic random-access memory (DRAM). HMCdelivers bandwidth and efficiencies while less energy is used totransfer data and provides a small form factor. In one embodiment of aHMC, the controller comprises a high-speed logic layer that interfaceswith vertical stacks of DRAM that are connected using TSVs. The DRAMhandles data, while the logic layer handles DRAM control within the HMC.

In other embodiments, a HMC may be implemented on, for example, amulti-chip module (MCM) substrate or on a silicon interposer. A MCM is aspecialized electronic package where multiple integrated circuits (ICs),semiconductor dies or other discrete components are packaged onto aunifying substrate thereby facilitating their use as a component (e.g.,thus appearing as one larger IC). A silicon interposer is an electricalinterface routing between one connection (e.g., a socket) and another.The purpose of an interposer is to spread a connection to a wider pitchor to reroute a connection to a different connection.

However, the DRAM stack in a HMC has more bandwidth and signal countthan many applications can use. The high signal count and high bandwidthof the DRAM stack in a HMC makes a cost effective host interfacedifficult.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a 72 bit vault for a flexible memory system accordingto an embodiment:

FIG. 2 illustrates a 36 bit vault for a flexible memory system accordingto another embodiment;

FIG. 3 illustrates a 36 bit vault for a flexible memory system accordingto another embodiment:

FIG. 4 illustrates a flexible memory system according to an embodiment:

FIG. 5 illustrates a block diagram of a computer system according to anembodiment:

FIG. 6 illustrates a block diagram of another computer system;

FIGS. 7a-b illustrate a flexible memory system according to anembodiment:

FIG. 8 is a plot showing the power savings according to an embodiment;and

FIG. 9 is a flowchart of a method for forming a flexible memory systemaccording to an embodiment.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass available equivalents ofthose claims.

A flexible memory system may be provided by tying vaults together (e.g.,above, within or below the DRAM stack) to create a solution with a lowcontact count while keeping a low power profile. Herein, contacts referto the leads, pins, solder balls or other types of interconnects thatcouple an integrated circuit to another device, such as a circuit board.Thus, leads, pins, solder balls or other types of interconnects may beused interchangeably.

The flexible memory system provides a range of solutions from no vaultstied together for the highest bandwidth to tying the available vaultstogether for a low contact count solution. The low contact countsolution can be applied to high density memory modules and low cost/lowpower system on a chip (SOC). FIG. 1 illustrates a 72 bit vaultinterface block 100 of a controller in a flexible memory systemaccording to an embodiment. The 72 bit vault interface block 100includes a command interface block (CIB) 110 and two data interfaceblocks (DIB) 120, 122. The CIB 110 includes contacts 112, includingcontacts for a first set of command signals, serial command signals anda second set of command signals. Two Data Interface Blocks (DIBs) 120,122 are also illustrated in FIG. 1. Each of the DIBs 120, 122 provides aplurality of contacts 124, including contacts for data input/output(I/O), the data bus and timing signals.

A DRAM die may be segmented into multiple autonomous partitions, e.g. 16partitions, e.g., see description of FIGS. 7A-B herein below. Eachpartition includes multiple independent memory banks, e.g., 2 to 8. Eachpartition is independent of the other partitions and autonomous in termsof data movement and command/addressing during normal operation. Memoryvaults are essentially vertically interconnected partitions which resultwhen partitioned DRAM die are stacked using TSVs and 3D integration. Thecommand interfaces of the vaults of the vault pair may be tied togethersuch that a vault pair shares a common command interface block of avault interface block (e.g., below the DRAM stack) to create a solutionhaving a low contact count while keeping a low power profile.

Considering ball grid arrays, for example, existing fine pitch flip-chiptechnologies may be used and may provide a 50 μm (130)×150 μm (132)contact pitch in a die package having a vault pitch in length 140 of1.35 mm and a width 142 of 1.8 mm. The vault interface block 100 may bematched in width to the effective DRAM vault pitch to minimize thefootprint on the controller.

FIG. 2 illustrates a 36 bit vault interface block 200 of a controller ina flexible memory system according to another embodiment. In FIG. 2, onecommand interface block (CIB) 210 having contacts 212 and one datainterface block (DIB) 220 having contacts 224 are shown. Contacts arerepresented by the unfilled circles. Existing fine pitch flip-chiptechnologies may be used to provide an appropriate contact pitch, e.g.,50 μm (230)×150 μm (232), in a die package having an appropriate vaultpitch, e.g., a length 240 of 0.9 mm and a width 242 of 1.8 mm.

FIG. 3 illustrates a 36 bit vault interface block 300 of a controller ina flexible memory system according to another embodiment. In FIG. 3, onecommand interface block (CIB) 310 having contacts 312 and one datainterface block (DIB) 320 having contacts 324 are shown. In theembodiment shown in FIG. 3, the contact field, which is the area of thedie where the contacts are located, may include 6 rows of contacts 350.Unused contacts are merely presented to show that a larger die may beused to provide a 36 bit vault. Using a 150 μm (330)×150 μm (332)contact pitch, The 36 bit vault interface block 300 may have a length340, e.g., of 0.9 mm, and width 342, e.g., of 1.8 mm. The area 360 ofthe total contact field may be 2.7 mm² (0.9 mm×3.0 mm).

FIG. 4 illustrates a flexible memory system 400 according to anembodiment. The flexible memory system 400 shown in FIG. 4 may include acontroller 410 having a number n of 72 bit vault interface blocks.However, those skilled in the art will recognize that alternative vaultinterface blocks may be implemented. Pairing vaults using eight 36 bitvault interface blocks uses 21.6 mm2 die area for the contact field(i.e., 2.7 mm2×8).

In FIG. 4, the controller 410 includes a number of n 72 bit vaultinterface blocks 420, 422, 424 similar to the 72 bit vault interfaceblock shown in FIG. 1. A 72 bit vault interface block 420, 422, 424 asshown in FIG. 4 may be implemented as vault interface block 100 as shownin FIG. 1. However, those skilled in the art will recognize otherimplementations of vault interface blocks may be used.

Each of the n 72 bit vault interface blocks 420, 422, 424 may include acommand interface block (CIB) 430 and two data interface blocks (DIB)440, 450. As described above, memory vaults may be formed by a stackedplurality of memory arrays and tied together (e.g., below the DRAMstack) to create a low contact count solutions while keeping a low powerprofile. As shown above with respect to FIG. 1, for example, existingfine pitch flip-chip technologies may be used to provide a contact pitchof 50 um×150 um contact pitch in a die package having an effective vaultlength of 1.35 mm and a width of 1.8 mm. However, those skilled in theart will recognize that alternative contact pitch, lengths and widthsmay be implemented. The vault interface blocks may be matched in widthto the effective DRAM vault pitch to minimize the footprint on thecontroller.

As shown in FIG. 4, the n vault interface blocks 420, 422, 424 areincluded in the controller 410 provide a total length of n times theindividual length of the vaults, e.g., n×1.35 mm=10.8 mm≈11.0 mm. Thus,the total area of the n vault interface blocks would be the total lengthtimes the width, e.g., 1.8 mm×11 mm=19.8 mm².

Memory 460 is also shown in FIG. 4. The memory 460 might comprisevertical stacks of DRAM die forming a DRAM hypercube 470. The verticalstacks of DRAM are connected together using through-silicon-via (TSV)interconnects (not shown, see FIGS. 8a-b ). Vaults 472, 474 of the DRAMhypercube 470 are tied together to form vault pair 490. Vaults 476. 478and vaults 480, 482 are tied together to form vault pairs 492, 494,respectively. Thus, a vault interface block (e.g., VIB 1 420) may serveboth pairs of vaults (e.g., Vault 1 472 and Vault 2 474) of a vault pair(e.g., vault pair 490). Although the preceding embodiments discuss tyingtogether pairs of vaults to share a vault interface block, embodimentsare not limited thereto, as any number of vaults might be tied togetherto share a vault interface block. Each pair of vaults is depicted assharing a command interface block.

The DRAM hybrid memory cube (HMC) 470 provides memory on the samesubstrate as a controller. As described above with reference to FIG. 1,each of the DIBs 440, 450 of vault interface block 420, for example, mayprovide contacts, including contacts for data input/output (I/O), thedata bus and timing signals. Logic blocks 498 may be associated witheach of the vault interface blocks 420. Logic may alternatively beprovided at the DRAM hypercube 470. An ASIC (see FIGS. 7a-b ) mayimplement logic blocks 498 associated with the vault interface blocks420. The logic blocks 498 provide host interface logic for processingsignals between a host and the DRAM hypercube 470. Data is handled bythe DRAM hypercube 470, while the logic blocks 498 handle control of theDRAM hypercube 470. For example, the number of contacts may be reducedby including timing logic 496. While shown separately in FIG. 4, thetiming logic may be included in logic blocks 498. Timing logic 496 maybe used to determine whether a request is destined to a particular oneof the vaults 472-482. In some embodiments, the timing logic 496 maycomprise timing and chip select logic.

A low power solution may be obtained by slightly increasing theindividual input/output (10 or I/O) buffer drive strength versusgenerating power for an interconnect that multiplexes vaults 472, 474,vaults 476, 478, and vaults 480, 482, respectively. Signal count can befurther reduced by combining the address/command bus with a data line(DQ) bus and use of a header. This resembles a packet interface to theDRAM hypercube 470. The first few clocks of the request involve acommand header. This is followed by write data for a write command. Avery low contact count solution is useful for large modules. Increasedbandwidth may be obtained through the use of multiple stacks. The buffercost and density of the module is driven by the signal count to the DRAMhypercube 470. Thus, a reduction in contact count reduces the buffercost and density.

Thus, the DRAM hypercube 470 provides a flexible method to configure ahost physical layer and multi-chip module (MCM) interconnect for a widerange of solutions. The highest bandwidth may be provided by not tyingall the vaults 470-782 together, whereas a low pin count solution may beprovided by tying all the vaults 470-782 together. Accordingly, the lowpin count solution can be applied to high density memory modules and lowcost/low power SOC's.

FIG. 5 illustrates a block diagram of a computer system 500 according toan embodiment. In FIG. 5, a CPU 510 is coupled to double data rate typethree (DDR type 3 or simply DDR3) dynamic random access memory (DRAM)520, 522. The CPU 510 is also coupled to a primary memory controller530, e.g., Northbridge. The primary memory controller 530 may include aPeripheral Component Interface (PCI) Express controller 540 and handlecommunications between the CPU 510, PCI-E (or accelerated graphicsprocessor (AGP)) video adapters 550, 552, 554, and a secondary memorycontroller 560.

FIG. 6 illustrates a computer system 600 according to an embodiment. InFIG. 6, the CPU 610 is coupled to the flexible memory system 620. Theflexible memory system includes a controller, such as a controllerimplemented in an application specific integrated circuit (ASIC) 630that includes logic blocks corresponding to vault interface blocks 640,and a DRAM hypercube 650. An ASIC 630 may be used to allow customizationfor a particular use, rather than using a general processor arranged forgeneral-purpose use. The flexible memory system 620 can be coupled tothe processor core through a high speed link 660, e.g., aserialize/deserialize (SERDES) data link. A high speed link 670 may alsobe used to couple the DRAM hypercube 650 to the ASIC 630.

FIGS. 7a-b illustrate a flexible MCM memory system 700 according to anembodiment. In FIGS. 7a-b , an ASIC 710 is mounted to a MCM substrate720. A DRAM hypercube 730 is also mounted to the MCM substrate 720.

The DRAM hypercube 730 may include multiple DRAM die 736 that arestacked using through-silicon vias (TSVs) 738. Signals from theconnections 712 of the ASIC 710 and the connections 732 of the DRAMhypercube 730 flow through blind vias that do not fully penetrate theMCM substrate 720. The blind vias only go deep enough to reach a routinglayer. Other signals from either the ASIC or DRAM which need to connectto the system through solder balls 722 will use vias that fullypenetrate the MCM substrate. The MCM memory system 700 provides aspecialized electronic package where multiple integrated circuits (ICs),semiconductor dies or other discrete components are packaged onto aunifying substrate, thereby facilitating their use as a component (e.g.,appearing as one larger IC). The ASIC 710 may also include logic blocks750 corresponding to vault interface blocks. The logic blocks 750 mayprovide host interface logic for processing signals between a host(e.g., CPU 710 in FIG. 7) and the DRAM hypercube 730 and control logicfor controlling the DRAM hypercube.

In some embodiments, the functionality of a logic layer may beimplemented at the ASIC 710, e.g., in logic blocks 750. Thus, the DRAMhypercube 730 may not include a high-speed logic layer coupled to thevertical stacks of DRAM 736. However, in other embodiments, the DRAMhypercube 730 may include a high-speed logic layer that is coupled tothe vertical stacks of DRAM 736.

The DRAM 736, along with the logic blocks 750, may handle data and DRAMcontrol within the hypercube 730. The TSVs 738 that pass through theDRAM 736 provide a high level of concurrent connections. Memory accessby the controller 710 is carried out on a highly efficient interface 780that supports high transfer rates, e.g., 1 Tb/s or more.

Referring to FIG. 7b , one or more of the plurality of stacked DRAM die736 may be segmented into multiple autonomous partitions 764, e.g. 16partitions. Each partition 764 includes multiple independent memorybanks, e.g., 2 to 8. Each partition 764 is independent of the otherpartitions and autonomous in terms of data movement andcommand/addressing during normal operation. Memory vaults 760, 762 areessentially vertically interconnected partitions 764 that result whenpartitioned DRAM die are stacked using TSVs 736.

Vaults 760, 762 of the DRAM hypercube 730 are paired to form vault pair770. Thus, the vault pair 770 serves one of vault interface blocks 1-8(e.g., 752) of the controller 710. However, those skilled in the artwill recognize that a different number of vault interface blocks may beimplemented. Moreover, vault blocks 1-8 may be tied together in pairs,fours, eights, etc., depending on the number of vault interface blocksto which they will be coupled, for example.

Referring to FIG. 4 and FIGS. 7a-b , clock signals may be reduced byincluding timing logic 496, whether on a separate logic layer in thehypercube 730 or on the DRAM 736 itself, as may be the case when aseparate logic layer is not included in the hypercube 730. Timing logic496 may snoop and analyze clock signals from ASIC 710 to identify avault targeted by a request, e.g., to determine whether a particularrequest is destined to a particular vault. For example, timing logic 496may determine that a request is destined to vault 760 rather than vault762. Responsive to identifying a targeted vault, the timing logic 496activates the targeted vault to receive the request and to return data.The timing logic 496 may thus reduce clock count by analyzing the clocksignals. Host interface logic block 750 may be used to save the adjusttiming for a clock signal targeted to an identified vault and adjust theclock signal according to the identified vault. The timing logic 496 isvery low power.

FIG. 8 is a plot 800 showing the power savings according to anembodiment. In FIG. 8, the flexible memory system 810 is compared to aDDR3 memory system 820 in terms of host physical power (PHY) 830 and theDRAM power 840. The flexible memory system 810 requires a host PHY power830 of approximately 1.5 watts 832 and requires a DRAM power 840 ofapproximately 2.5 watts 842. In contrast, the DDR3 memory system 820requires a host PHY power 830 of approximately 6.0 watts 834 andrequires a DRAM power 840 of approximately 33 watts 844. The flexiblememory system 810 has an area of 10 mm² 850 while the DDR3 memory system820 has an area of 21.2 mm² 860. Thus, the flexible memory system 810enables the implementation of a lower contact count while maintaining alower power profile than the DDR3 memory system 820.

FIG. 9 is a flowchart 900 of a method for forming a flexible memorysystem according to an embodiment. In block 910, a substrate is formed.In block 920, a plurality of vault interface blocks of an interfaceinterconnect are formed with a width associated with a pitch of a vaultof a DRAM. In block 930, a plurality of the vaults are tied together toreduce a contact count for the DRAM.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments that may bepracticed. These embodiments are also referred to herein as “examples.”Such examples can include elements in addition to those shown ordescribed. However, also contemplated are examples that include theelements shown or described. Moreover, also contemplate are examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

Publications, patents, and patent documents referred to in this documentare incorporated by reference herein in their entirety, just as ifindividually incorporated by reference. In the event of inconsistentusages between this document and those documents so incorporated byreference, the usage in the incorporated reference(s) are supplementaryto that of this document; for irreconcilable inconsistencies, the usagein this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim are deemed to fall within the scopeof that claim. Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to suggest a numerical order for their objects.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is to allow thereader to quickly ascertain the nature of the technical disclosure, forexample, to comply with 37 C.F.R. § 1.72(b) in the United States ofAmerica. It is submitted with the understanding that it will not be usedto interpret or limit the scope or meaning of the claims. Also, in theabove Detailed Description, various features may be grouped together tostreamline the disclosure. An unclaimed disclosed feature is not to beinterpreted essential to any claim. Rather, embodiments may includefewer features than those disclosed in a particular example. Thus, thefollowing claims are hereby incorporated into the Detailed Description,with an individual claim standing on its own as a separate embodiment.The scope of the embodiments disclosed herein is to be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. (canceled)
 2. A memory system, comprising: multiple DRAM memory diestacked above a substrate, wherein each die includes multiple partitionswhich operate independently from other partitions, and wherein multiplevertically interconnected partitions of the stack are interconnected toform multiple respective memory vaults; and a controller supported bythe substrate and configured to interface with a first memory vaultthrough a first group of data interface contacts, to interface with thesecond memory vault through a second group of data interface contacts,and to interface with at least the first and second memory vaultsthrough a shared group of command interface contacts.
 3. The memorysystem of claim 2, wherein the stack of multiple memory die comprisestiming logic arranged to analyze received clock signals to identify amemory vault targeted by a received request.
 4. The memory system ofclaim 3, wherein the timing logic is further configured to activate thetargeted vault in response to identifying the vault as being targeted bythe request.
 5. The memory system of claim 2, in which the controllerincludes logic blocks configured to provide host interface logic forprocessing signals between a host and the multiple stacked DRAM die. 6.A memory system, comprising: multiple DRAM memory die stacked above asubstrate, each die having multiple partitions which operateindependently from other partitions as to data movement, and whereinmultiple vertically arranged partitions of two or more die in the stackare interconnected by through silicon vias (TSVs) to form multiplerespective memory vaults; and a controller supported by the substrateand configured to interface, with partitions of a first memory vaultthrough a first group of data interface contacts, with partitions of asecond memory vault through a second group of data interface contacts,and with partitions of the first and second memory vaults through ashared group of command interface contacts.
 7. The memory system ofclaim 6, wherein the memory system comprises timing logic arranged tosnoop clock signals to determine a memory vault to which a request isdirected.
 8. The memory system of claim 6, wherein the controller isarranged to tailor timing for a clock signal for a targeted memoryvault.
 9. The memory system of claim 6, wherein the controller isconfigured to train timing for each memory vault.
 10. The memory systemof claim 6, wherein the memory system comprises timing logic arranged toanalyze clock signals received from the controller to identify a memoryvault targeted by a request.